1. Field of the Invention
The present invention relates to a polyethylenic foaming composition and a method of preparing the same, a polyethylene foam obtained from said polyethylenic foaming composition and a method of preparing the same, a molded composite foam comprising a foam layer obtained from a powder of said polyethylenic foaming composition and a non-foam layer obtained from a powder of a composition containing a certain thermoplastic elastomer and a method of preparing the same, a multilayer molded article consisting of a composite foam layer as said molded composite foam and a thermoplastic resin layer and a method of preparing the same, and a multilayer molded article consisting of a composite foam layer as said molded composite foam and a thermosetting resin layer and a method of preparing the same.
2. Related Art and Objective of the Invention
Synthetic resin foams are useful as materials for shock absorbers, heat insulators, packages and the like, and it is also known that such foams are produced by subjecting a vinyl chloride-based foaming composition powder to a powder molding process.
However, a foam obtained from a vinyl chloride-based foaming composition powder not only has poor lightness in weight, but also poor cleanness due to the emission of acidic substances upon burning as a waste, causing air pollution and acid rain.
We had already proposed that such problems could be overcome by replacing the vinyl chloride-based foaming composition powder with a polyolefinic foaming composition powder consisting of a thermoplastic elastomer as a partially crosslinked composition obtained from an ethylene/.alpha.-olefinic copolymeric rubber and a polyolefinic resin and a foaming agent of a thermal decomposition type for the purpose of obtaining a polyolefinic foam (JPA 345637-1992).
Nevertheless, such foam is not always satisfactory due to poor impact resilience, although it has a high expansion ratio and uniformly foamed cells.
On the other hand, an attempt was made to prepare a polyethylenic foam by press molding, extrusion molding, calender molding, and the like, using a foaming composition consisting of an ethylenic copolymer having functional groups such as carboxylic groups and carboxylic anhydride groups, an ethylenic copolymer having glycidyl groups, and a foaming agent of a thermal decomposition type (JPA 199630-1987).
However, a foam obtained by such methods suffers from the problems of a poor expansion ratio and poor impact resilience.
We expended much effort to obtain a synthetic resin foam having excellent lightness in weight, excellent cleanness, a high expansion ratio, and excellent impact resilience, and surprisingly found that by molding a particular foaming composition consisting of an ethylenic copolymer having glycidyl groups, a carboxylic acid having two or more carboxyl groups and a molecular weight of 1500 or less, and a foaming agent of a thermal decomposition type, a foam having a high expansion ratio and excellent impact resilience can be obtained. Then after further studies, we established the present invention.
On the other hand, a molded composite foam comprising a non-foam layer having a complex surface pattern such as a leather grain pattern and a stitch pattern and a foam layer has conventionally been employed as a skin for the interior of automobiles, and it is also known that such skin is made by subjecting a vinyl chloride-type non-foaming composition powder to a powder molding process to form a non-foam layer followed by molding a vinyl chloride-based foaming composition powder into a foam layer as a liner of the non-foam layer.
However, such molded composite foam obtained from a vinyl chloride-based resin not only has poor lightness in weight, but also poor cleanness, and thus is not satisfactory.
As a molded composite foam capable of overcoming such problems, we had already proposed a molded composite foam having a non-foam layer molded from a composition powder containing a thermoplastic elastomer which is a composition comprising an ethylene/.alpha.-olefinic copolymeric rubber and a polyolefinic resin or a thermoplastic elastomer which is a partially crosslinked composition comprising an ethylene/.alpha.-olefinic copolymeric rubber and a polyolefinic resin, and a foam layer molded from a foaming composition powder containing the thermoplastic elastomer mentioned above and a foaming agent of a thermal decomposition type (JPA-473-1993, 228947-1993 and 208467-1993).
Nevertheless, such molded composite foam has impact resilience which is not sufficient and which is not satisfactory, although it has excellent lightness in weight and excellent cleanness as well as a high expansion ratio of the foam layer.
We then made much effort to obtain a molded composite foam further having excellent impact resilience, and we surprisingly found that by using a particular foaming composition powder mentioned above consisting of an ethylenic copolymer having glycidyl groups, a carboxylic acid having two or more carboxyl groups and a molecular weight of 1500 or less, and a foaming agent of a thermal decomposition type as a foaming composition powder in the powder molding method, a molded composite having excellent impact resilience as well as a high expansion ratio can be obtained. Then after further studies, we established the present invention.
Accordingly, the present invention provides a polyethylenic foaming composition comprising (a) 100 parts by weight of an ethylenic copolymer having glycidyl groups consisting of 20 to 99.9% by weight of ethylene units, 0.1 to 30% by weight of the unit of a glycidyl ester of an unsaturated carboxylic acid or an unsaturated glycidyl ether, and 0 to 50% by weight of an ethylenic ester unit other than a glycidyl ester, (b) 0.1 to 30 parts by weight of a carboxylic acid having 2 or more carboxyl groups and a molecular weight of 1500 or less, and (c) 0.1 to 20 parts by weight of a foaming agent of a thermal decomposition type, and a method of preparing the same, as well as a polyethylenic foam molded from said polyethylenic foaming composition, and a method of preparing the same.
The present invention also provides a molded composite foam having excellent impact resilience, consisting of a foam layer obtained from the powder of said polyethylenic foaming composition (A) and a non-foam layer obtained from the powder of a composition containing a thermoplastic elastomer (B) described below, as well as a multilayer molded article having such molded composition foam and a method of preparing the same.
(B) is a thermoplastic elastomer having a complex dynamic viscosity .eta.*(1) of 1.5.times.10.sup.5 poise or less and a Newtonian viscosity index n of 0.67 or less, which is a composition consisting of an ethylene/.alpha.-olefinic copolymeric rubber and a polyolefinic resin or a partially-crosslinked composition consisting of an ethylene/.alpha.-olefinic copolymeric rubber and a polyolefinic resin.